The Obama administration soon will begin its systematic review of the approximately 300,000 pending deportation cases, separating "high priority" cases involving criminals it wants to deport from "low priority" cases it will drop, Homeland Security Secretary Janet Napolitano told Congress Wednesday.

The effort marks another point in an evolution of immigration enforcement away from the worksite raids of the Bush administration and towards deportations of illegal immigrants in prisons and jails. Napolitano said a group of Homeland Security and Justice Department officials will begin a small "pilot" review of immigration cases in "two or three" weeks, and hopes to rapidly expand its efforts.

Under the policy announced last year, federal immigration officials will place the highest priority on deporting illegal immigrants who pose a danger to public safety and national security, while "administratively closing" other cases, taking into consideration a list of factors. Those factors include the person's length of time in the United States, whether the immigrant arrived as a child, served in the military and has a spouse, child or parent who is a U.S. citizen. DHS officials say the new policy, which gives immigration officials "prosecutorial discretion," is similar to policies of previous administrations, and is a "common sense" approach to immigration enforcement.

But critics have blasted the policy, say that by "administratively closing" cases, the Obama administration is giving "amnesty" to illegal immigrants. The policy is "alarming, especially for those of us who firmly believe in the rule of law," Sen. Charles Grassley, R-Iowa, said Wednesday. Grassley said much is unknown about the policy, including whether illegal immigrants with criminal convictions will be eligible to stay in the country, and what will happen to undocumented immigrants whose cases are closed. "We want answers. We want transparency and accountability. We want to be part of the process," Grassley said.

In a recent speech, Napolitano said critics ignore the fact the number of deportations has increased during the Obama administration, and that the composition of that number has "fundamentally changed." The ranks of deported people "consist of more convicted criminals, recent border crossers, egregious immigration law violators and immigration fugitives than ever before," she said.

Of the 396,906 individuals removed from the U.S. in fiscal 2011, nearly 55 percent had been convicted of felonies or misdemeanors. That's an 89 percent increase of criminals from three years ago, DHS said. Napolitano said DHS has eliminated worksite raids, saying they "did nothing to enhance public safety." Instead, the Obama administration has focused on prosecuting employers who violate employment laws, she said.

Napolitano said the department's focus on criminal illegal immigrants is better than "the ad hoc approach where non-criminal aliens are more likely to be removed than criminals."